This invention relates to improvements in waste water discharge systems, particularly filtered discharge systems for filtering discharge from high solids-content waste water such as encountered in a septic tank. More particularly, the invention relates to improvements in filtered discharge systems including the provision of incremental liquid dischare apparatus, such as positive pressure pumps or siphons, emplaced within the septic tank and means for filtering even relatively small solid particles from the discharged liquid while resisting clogging by those solids.
In the past, mechanical filtering devices placed within the septic tanks have been generally unsuccessful because the filter quickly becomes clogged by the solids present in the tank. However some degree of filtering is often necessary, especially in those septic tanks which discharge into drainfields. Failure to filter the larger solids from the liquid dischare eventually causes a clogged drainfield, which is generally much more expensive to correct than a clogged filter.
A partial solution to this problem used in many septic tanks is to place the mouth of the discharge pipe at a selected level within the septic tank to avoid most of the solids. This practice is based upon the propensity of most solids within a septic tank to either sink to the bottom and form a "sludge" layer or rise to the top of the liquid and form a "scum" layer. The liquid between these layers is relatively "clear." Prior art systems, including those shown in U.S. letters Pat. Nos. 2,482,353, 1,408,810 and 1,150,510, recognize this concept and place the mouth of the discharge pipe within the relatively "clear" area. However, even in this clear area, a screen or filter placed over the mouth of the discharge pipe would generally become quickly clogged because the force of the flow through the discharge pipe would impact solids, which are suspended in the liquid, upon the screen.
Probably the most successful device to date for filtering discharge from septic tanks is a filter manufactured under the trademark GO CATCHIT by Go General Equipment and Manufacturing Co., Inc. However such filter does not facilitate the use of "dosing" discharge devices in septic tanks, nor does it utilize certain advantageous anticlogging structural features, all to be discussed further hereafter.
A common method of discharging a septic tank into a drainfield is characterized by a slow "dribbling" of the outflow caused by the rising level within the tank. This "dribbling" method, combined with the passage of solids into the drainfield, has a marked propensity to clog the drainfield. It has long been recognized that discharging the effluent from the tank in relatively large incremental "doses" is superior to "dribbling" because the increased velocity of the dose spreads the solids-carrying liquid more evenly throughout the drainfield and does not have as much of a tendency to clog the upstream portion of the drainfield as does the practice of "dribbling." Also the alternate "load and rest" cycles characteristic of dosing increases the percolation capacity of the drainfield.
One device for discharging predetermined increments of liquid from a septic tank is a dosing siphon. However the dosing siphon cannot be placed within the septic tank itself because the large pipe diameters capable of passing large solids to prevent clogging of the siphon require a large liquid level differential or "head" to create the pressure necessary to activate the siphon. The large liquid level differential or "head" applied to a typical septic tank with considerable area would result in the discharge of an excessively large volumetric dose, possibly overwhelming the capacity of a typical drainfield. Construction of a larger drainfield capable of handling the large volumetric dose delivered by a dosing siphon discharge would be impracticably expensive. Consequently, a dosing siphon is typically placed in an additional exterior vault, considerably smaller in horizontal cross section than the septic tank, so that the large liquid level differential or "head" does not result in such a large incremental dose. A major shortcoming of this arrangement is that the discharge, although delivered to the drainfield in incremental doses, is still not filtered to remove solids which would tend to clog the drainfield. Moreover, the exterior vault constitutes a considerable added expense, and this arrangement can only be used on sloping lots since the vault and dosing siphon require additional vertical drop between the septic tank discharge and the drainfield.
A "trigger trap" has been used with dosing siphons in some nonwaste water applications to decrease the liquid level differential or "head" which is required to activate the dosing siphon. The trigger trap is comprised of a pipe, considerably smaller than that used for the dosing siphon, which interconnects with the dosing siphon in such a manner as to break the airlock and activate the dosing siphon with a smaller "head." The use of a trigger trap would permit a dosing siphon to be placed within a septic tank and discharge a sufficiently small increment of effluent which could be adequately dispersed by a typical drainfield. However the small pipe comprising the trigger trap would be typically clogged or blocked by the solids present in a septic tank. Except for the aforementioned clogging problem of the "trigger trap," a dosing siphon with a trigger trap, economically located within a septic tank, rather than exterior thereto, would effectively discharge sufficiently small predetermined incremental doses of effluent into the drainfield.
Another method of discharging predetermined incremental doses of effluent from a septic tank is a submersible pump which employs a switch adapted to activate and deactivate the pump according to the level of the surrounding liquid. Pumps are also necessary in positive pressure sewer systems wherein the liquid discharge, instead of flowing through a drainfield, is pumped to a disposal facility. Positive pressure sewer systems are particularly useful in areas which are not suitable for a drainfield and do not have an established gravity sewer system. Such pressure sewer systems can be less costly to build than gravity sewers because the pipes may be smaller and most importantly do not have to be installed to grade. A major drawback to pressure sewer systems however is the large-tolerance, inefficient pumps necessary to pass solids. Pumps placed unprotected in a septic tank require large clearances to pass solids, and are therefore inherently inefficient, requiring more power and larger size than if pumping clear liquid.
Accordingly, what is needed is a filtered waste water discharge system which is capable of enclosing an incremental fluid discharge device such as a pump, or dosing siphon with trigger trap, within a septic tank and preventing the discharge of solids without becoming clogged or blocked by these solids. A small screen covering the intake of these fluid discharge devices would rapidly become blocked by the force of the flow and the solids suspended in the liquid, even in the relatively clear layer. Even a larger screen, enclosing the entire fluid discharge device, would also eventually become blocked from the suspended solids in the clear area and from contact with the "scum" and "sludge" layers.